1. Field of the Invention
The present invention relates to a semiconductor chip package and a fabrication method thereof.
2. Description of the Related Art
Technology to fabricate a several hundred μm size micro structure using micro machining technology, such as semiconductor micro processing technology, has been developing. For example, application of this technology to various sensors, optical switches in the optical communication field and radio frequency (RF) components has begun.
Such micro structures can be fabricated using a conventional semiconductor fabrication process, so that it can be integrated into a single chip.
A chip on which a system having specific functions, including this micro structure, is constructed is called a Micro-Electrical-Mechanical System (MEMS) chip, or a Micro-System-Technology (MIST) chip (hereafter simply called an MEMS device). One example of known MEMS devices is an acceleration sensor, and disclosed in Japanese Patent Application Kokai (Laid-Open) No. 11-135804.
The piezo acceleration sensor chip disclosed in Japanese Patent Application Kokai No. 11-135804 has a frame. This frame includes a center section and beam sections. The beam sections extend between the inner side face of the frame and the center section. The weight section is supported in the center section such that the weight section can oscillate. The support member supports the bottom face of the frame, and encloses the outer edge of the weight section via notches.
The weight section is an element that is moved by external force (stress), so that it is also called a “movable section” or “movable element.” The movable element and the beams are integrated into a micro structure. Each beam is thin and narrow.
The sensor chip having this configuration is generally provided as a packaged device.
An example of conventional acceleration sensor chip packages will now be described with reference to FIGS. 9A and 9B of the accompanying drawings.
FIG. 9A is a plan view depicting the composing elements of a conventional acceleration sensor chip package. To show the internal configuration, an illustration of the top face of the protective cover (will be described) is omitted.
FIG. 9B is a cross sectional view taken along the dashed line 9B-9B in FIG. 9A.
This acceleration sensor chip package 100 has an acceleration sensor chip 110. The acceleration sensor chip 110 has a plurality of electrode pads 112. The electrode pads 112 are pads for supplying signals to another element from the acceleration sensor chip 110 or introducing signals to the acceleration sensor chip 110. In the acceleration sensor chip 110, a movable structure 114, which operates mechanically, is built in.
The acceleration sensor chip 110 also has a sealing substrate 116 which seals and restricts the movement of the movable structure 114. This sealing substrate 116 is bonded to the substrate 120 by adhesive material 122.
The protective cover 130 has a turned bowl shape. On the substrate 120, the lower edge of the protective cover 130 is bonded. The protective cover 130 and sealing substrate 116 constitute a closed space 140 for sealing the acceleration sensor chip 110.
At the edges of the substrate 120, external terminals 150 are provided. The external terminals 150 extend to the outside from inside the closed space 140. In the closed space 140, the external terminals 150 and the electrode pads 112 of the sensor chip 110 are electrically connected to each other by bonding wires 160.
In order to seal the entire chip by mold resin without interfering with the operation of the detecting section of the acceleration sensor, a structure to create a frame-shaped “mold resin inhibited area” around the detecting section is used. Such structure is disclosed in Japanese Patent Application Kokai No. 7-225240.
According to the above described acceleration sensor chip package, the acceleration sensor chip and external terminals are electrically connected by the bonding wires. The protective cover is used to contain the bonding wires and to seal the acceleration sensor chip. Therefore, seal-by-potting using transfer mold or liquid resin cannot be performed, and the area of the package increases.
In the fabrication method of the conventional sensor chip package, the acceleration sensor chip is diced and then packaged. Thus, the cutting chips created during the dicing process may attach to the movable (weight) element and its vicinity. This will hinder the operation of the movable element.
As Japanese Patent Application Kokai No. 7-225240 discloses, for example, attaching a special member to the acceleration sensor chip makes the fabrication steps more complicated. This worsens the throughput not only of the acceleration sensor chip, but also of the acceleration sensor chip package, which is the final product.
Therefore a technology for further downsizing the acceleration sensor chip package, and a technology for improving yield and productivity, particularly by preventing damage of the movable element when the acceleration sensor chip package is fabricated, and implementing simplifier fabrication steps are desired.